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Construction of electronic cigarettes
An electronic cigarette is a handheld battery-powered vaporizer that simulates smoking, but without tobacco combustion. E-cigarette components include a mouthpiece (drip tip2), a cartridge (liquid storage area), a heating element/atomizer, a microprocessor, a battery, and some of them have an LED light on the end.3 An exception to this are mechanical e-cigarettes (mods) which contain no electronics and the circuit is closed by using a mechanical action switch.4 An atomizer consists of a small heating element, or coil, that vaporizes e-liquid and a wicking material that draws liquid onto the coil.5 When the user inhales a flow sensor activates the heating element that atomizes the liquid solution;6 most devices are manually activated by a push-button.7 The e-liquid reaches a temperature of roughly 100–250 °C (212–482 °F) within a chamber to create an aerosolized vapor.8 The user inhales an aerosol, which is commonly but inaccurately called vapor, rather than cigarette smoke.9 Vaping is different than smoking, but there are some similarities, including the hand-to-mouth action of smoking and a vapor that looks like cigarette smoke.1 The aerosol provides a flavor and feel similar to tobacco smoking.1 A traditional cigarette is smooth and light but an e-cigarette is rigid, cold and slightly heavier.1 There is a learning curve to use e-cigarettes properly.10 E-cigarettes are cigarette-shaped,11 and there are many other variations.12 E-cigarettes that resemble pens or USB memory sticks are also sold that may be used unobtrusively. There are three main types of e-cigarettes: cigalikes, looking like cigarettes; eGos, bigger than cigalikes with refillable liquid tanks; and mods, assembled from basic parts or by altering existing products.14 Cigalikes are either disposable or come with rechargeable batteries and replaceable nicotine cartridges.15 A cigalike e-cigarette contains a cartomizer, which is connected to a battery.16 A "cartomizer" (a portmanteau of cartridge and atomizer17) or "carto" consists of an atomizer surrounded by a liquid-soaked poly-foam that acts as an e-liquid holder.5 Clearomizers or "clearos", not unlike cartotanks, use a clear tank in which an atomizer is inserted.18 A rebuildable atomizer or an RBA is an atomizer that allows the user to assemble or "build" the wick and coil themselves instead of replacing them with off-the-shelf atomizer "heads".19 The power source is the biggest component of an e-cigarette,20 which is frequently a rechargeable lithium-ion battery.12 As the e-cigarette industry continues to evolve, new products are quickly developed and brought to market.21 First-generation e-cigarettes tend to look like traditional cigarettes and so are called "cigalikes".19 Most cigalikes look like cigarettes but there is some variation in size.16 Second-generation devices are larger overall and look less like traditional cigarettes.22 Third-generation devices include mechanical mods and variable voltage devices.19 The fourth-generation includes sub ohm tanks and temperature control devices.23 The voltage for first-generation e-cigarettes is about 3.724 and second-generation e-cigarettes can be adjusted from 3 V to 6 V,25 while more recent devices can go up to 8 V.24 The latest generation of e-cigarettes are pod mods,26 which provide higher levels of nicotine than regular e-cigarettes27 through the production of aerosolized protonated nicotine.28 E-liquid is the mixture used in vapor products such as e-cigarettes29 and usually contain propylene glycol, glycerin, nicotine, flavorings, additives, and differing amounts of contaminants.30 E-liquid formulations greatly vary due to fast growth and changes in manufacturing designs of e-cigarettes.16 The composition of the e-liquid for additives such as nicotine and flavors vary across and within brands.31 The liquid typically consists of a combined total of 95% propylene glycol and glycerin, and the remaining 5% being flavorings, nicotine, and other additives.32 There are e-liquids sold without propylene glycol,33 nicotine,34 or flavors.35 The flavorings may be natural, artificial,31 or organic.36 Over 80 chemicals such as formaldehyde and metallic nanoparticles have been found in the e-liquid.37 There are many e-liquids manufacturers in the US and worldwide,38 and more than 15,500 flavors existed in 2018.39 Under the US Food and Drug Administration (FDA) rules, e-liquid manufacturers are required to comply with a number of manufacturing standards.40 The revision to the EU Tobacco Products Directive has some standards for e-liquids.41 Industry standards have been created and published by the American E-liquid Manufacturing Standards Association (AEMSA).